6-hydroxy-1H-pyrimidin-4-one

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1995-09-04 to 1995-12-18

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: - Minor methodological deficiencies although study was conducted under GLP. - Minor deficiencies in reporting.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Deviations:

yes

Remarks:

: no documentation if reference substance tested, initial biomass concentration deviates from guideline but growth was constant during test period in control, quantification of cell number conducted photometrically, correlation of OD and cell numbers not

Qualifier:

equivalent or similar to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

Deviations:

yes

Remarks:

see deviations under OECD Guidance 201

Principles of method if other than guideline:

- Cell numbers were determined photometrically. To this end, absorption was measured at 685 nm and converted into the parameter "cell number/mL" by use of a calibration curve. The respective correlation between cell number and absorption was not documented in the report.
- Incubation with a reference substance to prove the applicability of the test system, as required by the guideline, was not documented.

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: A stock solution of 1 g/L was prepared.

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

TEST ORGANISM
- Strain: Scenedesmus subspicatus CHODAT (86.81 SAG
- Source (laboratory, culture collection): Institut fur Wasser-, Boden- and Lufthygiene, Berlin
- Age of inoculum (at test initiation): 3 days
- Method of cultivation: The test cultures were prepared from a stock culture 3 days before start of the test at a concentration of 20'000 cells/mL.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Post exposure observation period:

No post-observation was performed.

Test temperature:

22.9-23.3°C in a temperature controlled room

pH:

at start of the test: 5.3-8.6
at end of the test: 5.2-9.6
In some cases, the quite low pH at the start of the study (caused by the acidic property of the test item) raised during the test.

Nominal and measured concentrations:

Nominal concentrations of the test item were reported throughout the test as stability of the test item in water was proven (see also table 1).
Nominal concentrations: 5, 9, 15, 26, 45, 78, 135 mg/L.

Details on test conditions:

TEST SYSTEM
- Test vessel: Erlenmeyer flasks
- Aeration: yes
- Initial cells density: 20'000 cells/mL
- Control end cells density: 1'130'000
- No. of vessels per concentration (replicates): 5
- No. of vessels per control (replicates): 8

GROWTH MEDIUM
- Standard medium used: yes

OTHER TEST CONDITIONS
- Sterile test conditions: yes
- Adjustment of pH: no
- Light intensity and quality: approximately 8000 Lux, white

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: colorimeter at 685 nm
- Chlorophyll measurement: presumably yes

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 1.7
- Test concentrations: 5, 9, 15, 26, 45, 78, 135 mg/L

Reference substance (positive control):

no

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

15 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

cell number

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

37 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

cell number

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

11 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

cell number

Duration:

72 h

Dose descriptor:

EC90

Effect conc.:

128 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

cell number

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

105 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

21 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

The results of the test are depicted in table 2.

Table 2: Cell numbers of Scenedesmus subspicatus after treatment with the test item. Reported values are means.

Nominal concentration [mg/L]	Cell number [10'000 cells/mL]
	at 0h	24h	48h	72h
0 (control)	2^#	9	31	113
5	2^#	10	33	114
9	2^#	9	27	94
15	2^#	10	31	100
26	2^#	8	23	73
45	2^#	5	10	36
78	2^#	5	6	15
135	2^#	6	7	15

^#theoretical values

 

 

Table 3: Area under curve (AUC) for growth rate, growth rates, and pH in dependance on the different test item concentrations.

Method		0 mg/L	5 mg/L	9 mg/L	15 mg/L	26 mg/L	45 mg/L	78 mg/L	135 mg/L
AUC	Area	91.5	95	78	86	62.5	28	13.5	15.5
	% inhibition		-3.8	14.8	6	31.7	69.4	85.2	83.1
growth rate 0-72h	growth rate 0-72h	1.345	1.348	1.283	1.304	1.199	0.963	0.672	0.672
	% inhibition		-0.2	4.6	3	10.9	28.4	50	50
pH	at 0h	8.6	8.6	8.5	8.3	7.4	6.7	5.9	5.3
	at 72h	7.2	9.6	9.5	9.2	8.9	8.5	6.8	5.2

 

Validity criteria fulfilled:

yes

Conclusions:

Incubation of the algae Scenedesmus subspicatus with the test item 4.6-dihydroxypyrimidin (CAS 1193-24-4) resulted in inhibition of algal growth. The 72h EC50 (cell number) was 37 mg/L, the 72h EC50 (growth rate) was 105 mg/L. The NOEC, based on cell number was calculated to be 15 mg/L.

Executive summary:

The aquatic toxicity of 4.6-dihydroxypyrimidin (CAS 1193-24-4) was determined by means of an algal growth inhibition test similar to OECD Guideline 201 and EU Method C.3.

Incubation of the algae (Scenedesmus subspicatus) with the test item 4.6-dihydroxypyrimidin (CAS 1193-24-4) resulted in inhibition of algal growth. The 72h EC50 (cell number) was 37 mg/L, the 72h EC50 (growth rate) was 105 mg/L. The NOEC, based on cell number was calculated to be 15 mg/L.

Description of key information

ErC50=105 mg/L, 72h, (growth rate), Scenedesmus subspicatus, similar to OECD 201, Scholz 1995
ErC10=21 mg/L, 72h, (growth rate), Scenedesmus subspicatus, similar to OECD 201, Scholz 1995

Key value for chemical safety assessment

EC50 for freshwater algae:

105 mg/L

EC10 or NOEC for freshwater algae:

21 mg/L

Additional information

The aquatic toxicity of the test substance was determined by means of an algal growth inhibition test similar to OECD Guideline 201 and EU Method C.3, with some deviations. The test was performed under GLP.

The study is considered to be reliable with restrictions. The results are adequate for risk assessment, classification and labeling.